An energy-resolved study of the fragmentation of ionized 1-Penten-3-ol

A detailed energy-resolved study of the fragmentation of CH₂?CHCH(OH)CD₂CD₃ (1-d₅) has been carried out using metastable ion studies and charge exchange techniques, combined with collision-induced dissociation studies to establish the structures of fragment ions. At low internal energies (metastable ions) the molecular ion of 1-d₅ rearranges to the 3-pentanone structure and fragments by loss of C₂H₅ or C₂D₅ leading to the acyl structure, [CH₃CH₂C?O]⁺ or [CD₃CD₂C?O]⁺, for the fragment ion. However, with increasing internal energy of the molecular ion this rearrangement process decreases rapidly in importance and loss of C₂D₅ by direct cleavage, leading to [CH₂?CHCH?OH]⁺, becomes the dominant fragmentation reaction. As a result the [C₃H₅O]⁺ ion seen in the electron impact mass spectrum of 1-penten-3-ol has predominantly the protonated acrolein structure.     

Electron impact ionization mass spectra of some substituted dipyrido[1,2-a:4,3-d]pyrimidinones

The electron impact ionization mass spectra of dipyrido [1,2-a:4,3-d]pyrimidinones are strongly influenced by the degree of aromaticity of the fused rings. The molecular ions of the compounds are fairly stable. The main routes of fragmentation involve formation of the [M – H]⁺ ion and loss of substituents, H₂CN˙, CO and alkyl radicals.     

The effect of para-substitution on the mass spectra of arylsulphonate esters of neopentanol

The mass spectra of several para-substituted benzenesulfonic and benzoic esters of unlabelled and 1,1-d₂-neopentyl alcohol are examined and compared. Evidence is presented of migration of the aryl group from the sulfur to an oxygen atom in the molecular ions of the sulfonic esters. The nature of the fragmentation processes and the occurrence of metastable ions for these processes are both much more dependent upon the polarity of the para substituent in the case of the sulfonates than for the benzoates. Elimination of C₅H₁₀ occurs from the molecular ion of the p-methoxysulfonate with transfer to the residual ion of a hydrogen atom selected randomly from the alkyl fragment, while in the case of the p-aminosulfonate, incomplete randomization is demonstrated.     

Stereoselective Glycosidic Coupling Reactions of Fully Benzylated 1,2-Anhydro Sugars with N-Tosyl- or N-Benzyloxycarbonyl-l-serine Methyl Ester

Abstract

The glycosidic coupling reaction of 1,2-anhydro-3,4,6-tri-O-benzyl-β-d-mannopyranose (7), 1,2-anhydro-3,4,6-tri-O-benzyl-α-d-galactopyranose (21), and 1,2-anhydro-3,4-di-O-benzyl-α-d-xylopyranose (18) with N-tosyl- (10) or N-benzyloxycarbonyl- (11) L-serine methyl ester provides a new stereocontrolled synthesis of 1,2-trans linked glycopeptides. The 1,2-anhydro sugars are shown to react smoothyl with 10 or 11 in the presence of Lewis acid (ZnCl₂ or AgOTf) as well as powdered 4A molecular sieves in CH₂Cl₂ at room temperature to afford glycosyl serine derivatives with high stereoselectivity and high yield in less than 30 min. An improved method using 2-O-acetyl-3,4,6-tri-O-benzyl-α-d-mannopyranosyl chloride (6) as the key intermediate for ring closure was applied for the synthesis of 1,2-anhydro-3,4,6-tri-O-benzyl-β-d-mannopyranose.     

The elimination of metal(I) hydride in the mass spectra of some metal(II) compounds

Metal(I) hydrides are eliminated as neutral species in the electron impact ionization mass spectra of copper(II) and palladium(II) complexes of ethylene-N,N′-3-benzoylprop-2-en-2-amine. Deuterium labelling shows that the hydrogen atom of the metal(I) hydride is derived predominantly from the ethylene bridge both for ion source reactions and for metastable ion transitions. Evidence supporting the proposed rationalization for elimination of metal(I) hydride is provided by the observation of an analogous reaction in the mass spectrum of (ethylene-N,N′-salicylaldiminato)copper(II). The mass spectrum of ethylene-d₄-N,N′-3-benzoylprop-2-en-2-amine shows an unusual rearrangement to give [C₇H₅D₂]⁺ ions involving a formal phenyl-to-methylene transfer.     

Charge Localization: Doubly-Charged Ion Reactions in Toluene

The kinetic energy released in the major charge-separation reactions of [C₇H₈]⁺⁺ [C₇H₇]⁺⁺ and [C₇H₆]⁺⁺ formed from toluene, and in the corresponding reactions of toluene-α-d₃, toluene-d₈ and 2,3,4,5,6-toluene-d₆ has been measured. Some fragmenting [C₇]⁺⁺ ions are linear; in certain cases they have cyclic structures while in others ‘coiling’ of a linear ion to allow hydrogen transfer in the transition state is suggested. From relative metastable ion abundance data it is apparent that nearly complete H/D randomization accompanies these slow reactions.     

Mass spectra of substituted and annelated benzofurazan-1-oxides

Electron impact positive ion spectra of ten substituted or annelated benzofurazan-1-oxides are reported. While most of the molecular ions lose either NO˙ + NO˙, or NO˙ + CO, some also lose CO as an initial fragment. One of the fragmentation pathways for 4-methylbenzofurazan-1-oxides involves initial ˙CHO loss. With the annelated benzofurazan-1-oxides (naphtho[1,2-c]furazan oxide and quinolo[3,4-c]furazan oxide), loss of N₂O₂ is followed by a retro-Diels–Alder elimination of butadiyne or propynenitrile, respectively from the aryne radical cation. In the case of quinolo[5,6-c]furazan oxide, loss of N₂O₂ from the molecular ion must be followed by substantial rearrangement to enable the observed loss of propynenitrile to take place.     

N-Amino Derivatives of Condensed Imidazole Systems

The previously unknown 1-amino- and 3-aminonaphtho[1,2-d]imidazoles, 1-aminonaphtho[2,3-d]imidazole, 1-aminophenanthro[9,10-d]imidazole and the N-amino-N'-methylimidazolium picrates corresponding to them have been obtained by direct amination of a series of condensed imidazoles with O-picrylhydroxylamine. An X-ray structural investigation of 1-amino-3-methylnaphtho[1,2-d]imidazolium picrate showed that, in difference to 1-aminobenzimidazolium salts, a conformation exists in it in which the hydrogen atoms of the N-NH₂ group are directed to the side of the meso carbon atom.     

A new mass spectrometric method for determining the degree of labeling with heavy isotopes: The study of deuterated toluenes

A new method of general applicability for determining the percentage deuterium labeling in organic compounds is described. It uses the heights of ‘metastable peaks’ in the mass spectrum to determine the relative amounts of deuterated and undeuterated species. The method is illustrated by describing the analysis of mixtures of toluene-o-d₁ and toluene, of toluene α-d₁ and toluene, and of toluene-2,6-d₂, toluene-o-d₁ and toluene.     

Synthesis of some novel tetracyclic imidazole derivatives

Representatives have been made of three new heterocyclic systems (IIH) containing an imidazole ring. Synthetic routes are described for compounds of type II where X = CH₂ (8H-dibenzo[3,4: 6,7]cyclohept[1,2-d] imidazoles), and X = CH₂CH₂ (8,9-dihydrodibenzo[3,4:7,8]cyclooct[1,2-d] imidazoles) and X = S (dibenzo[2,3:6,7] thiepin] 4,5-d] imidazoles). In addition, improved syntheses are presented for some previously known compounds employed as intermediates in this work.     

A feature of the fragmentation mechanism of exo-2-norbornyl chloride. Stereoselective hydrogen atom abstraction revealed by metastable ion studies

The position of deuterium in the products of the addition of HCL and DCI to exo 5, 6-d₂ norbornene has been determined mass spectrometrically by measuring metastable ion abundances. The results show a stereo-selective hydrogen atom abstraction when the molecular ion of exo-2-norbornyl chloride fragements by loss of a chloroethyl radical.     

Tetracyclic phenothiazines. VII. Electron impact promoted mass spectral fragmentation of some pyrido[3,2,1-kl]phenothiazines

The mass spectral fragmentation pattern of a series of pyrido[3,2,1-kl]phenothiazines is reported. The major fragments are derived from the breakdown of the pyrido ring and substituents thereon. The 1,2-/2,3-unsaturated, unsubstituted and most of the 3-substituted compounds show the molecular ion as the base peak indicative of their relative stability toward electron impact. The genesis of the base peaks from the molecular ions of the 2,2-dithiophenyl substituted compounds probably involves a concerted expulsion of a neutral diphenyldisulfide molecule and hydrogen atom transfer from the 1-position to the 2-position in the pyrido ring. On the other hand, 2-thiophenyl substituted molecular ions lead to base peaks involving simultaneous ring opening of the pyrido ring, cleavage of phenylthiomethylene moiety as a radical and contractive ring closure to the pyrrole system. These two mechanisms appear to be diagnostic for distinguishing 2,3- versus 2,2-positional isomers. The McLafferty rearrangement takes place in the 2-thiophenyl and 2,2-dithiophenyl substituted compounds. The retro-Diels-Alder fragmentation of the pyrido ring occurs in varying degrees depending on the nature of the 2- and 3- substituents and also the presence or absence of unsaturation in the pyrido ring. In the 2-thiophenyl-3-keto compounds, thiophenyl group participation with 3-carbonyl carbon and oxygen atoms is observed in the genesis of some interesting ion fragments. The detection of metastable ions in the spectra of 1,2-dihydro-2-thiophenyl-, 1,2-dihydro-2,2-dithiophenyl-3-hydroxy-, and 1,2-dihydro-2,2-dithiophenyl-3-keto-3H-pyrido[3,2,1-kl]phenothiazines; and spectra of 1,2-dihydro-3-methyl-, 1,2-dihydro-2-carbethoxy-3-keto- and 1,2-dihydro-2-thiophenyl-3-keto-3H-pyrido[3,2,1-kl]pheno-thiazines at low voltage support major fragmentation pathways.     

Fragmentation of deprotonated d-ribose and d-fructose in MALDI—Comparison with dissociative electron attachment

We present a detailed, collaborative study on the fragmentation of deprotonated native d-ribose and d-fructose and the isotopically labelled 1-¹³C-d-ribose, 5-¹³C-d-ribose and C-1-d-d-ribose. The fragmentation is studied in a matrix assisted laser desorption/ionization time of flight mass spectrometer (MALDI ToF MS), both in in-source decay (ISD) and post-source decay (PSD) mode and compared with fragmentation through dissociative electron attachment (DEA). Fragmentation of deprotonated monosaccharides formed in the MALDI process, as well as their transient molecular anions formed upon electron attachment are characterized by loss of different numbers of H₂O and CH₂O units. Two different fragmentation pathways leading to cross-ring cleavage are identified. Metastable decay of deprotonated d-ribose proceeds either via an X-type cleavage yielding fragment anions at m/z = 119, 100 and 89, or via an A-type cleavage resulting in m/z = 89, 77 and 71. A fast and early metastable cross-ring cleavage of deprotonated d-ribose observed in in-source decay is dominated by X-type cleavage leading mainly to m/z = 100 and 71. For dissociative electron attachment to d-ribose a sequential dissociation was identified that includes metastable decay of the dehydrogenated molecular anion leading to m/z = 89. All other fragmentation reactions in DEA to d-ribose are likely to proceed directly and on a faster timescale (below 400 ns).     

Destabilized carbenium ions: Secondary and tertiary α-carbomethoxybenzyl cations

The secondary α-carbomethoxybenzyl cations a and the tertiary α-carbomethoxybenzyl cations d have been generated by electron impact-induced fragmentation from appropriately α-substituted methyl phenylacetate and 2-phenylpropionates 1–4. The ions a and d are further examples of destabilized carbenium ions with a push–pull substitution at the carbenium ion centre. The characteristic reaction of these ions is a rearrangement by a 1,2-shift of the methoxy group concomitant to the elimination of CO. This rearrangement reaction is associated with a very large and non-statistical kinetic energy release (a : T ₅₀ = 570 meV; d : T ₅₀ = 760 meV), which is attributed to tight transition states along the reaction coordinates corresponding to the three-membered cyclic oxonium ions b and h, respectively. The tertiary ion d can be distinguished from its more stable isomers f and g by the mass-analysed ion kinetic energy and collisional activation spectra. The investigation of specifically deuterated analogues of ions d and g reveals an isomerization of d to g via a species protonated at the phenyl group but no equilibration between d and g. This isomerization exhibits a large isotope effect for the hydrogen transfer, indicating similar energy barriers for the isomerization and for the CO elimination of d.     

The structures of [C5H5O]+ ions formed from isomers of nitrophenol in the gaseous phase

Translational energy release measurments on metastable ions are used in the comparison of the structures of isomeric ions. Metastable ions, m₂⁺, formed from m₁⁺ ions as the result of a high energy process in the ion source are compared with isomeric metastable ions formed as daughters from fragmentation of metastable m₁⁺ ions in a field. In the case of o-, m- and p-nitrophenol the structure of the [C₅H₅O]⁺ ions formed from [C₆H₅O]⁺ ions by these two independent methods is different as verified by comparison of the behaviour of [C₅H₅O]⁺ ions formed from several other compounds.     

Solvothermal synthesis,crystal structure and magnetic properties of the one-dimensional coordination polymer Ni(DMBDIZ)(OOCMe)2 (DMBDIZ = 2,6-dimethylbenzo[1,2-d:4,5-d′]diimidazole)

The solvothermal synthesis and crystal structure of the one-dimensional coordination polymer Ni(DMBDIZ) (OOCMe)₂ (DMBDIZ = 2,6-dimethyl-benzo[1,2-d:4,5-d]diimidazole) are described. Each nickel ion is located in pseudo-octahedral geometry formed by four oxygen atoms from two bidentate acetate anions and two trans-related tertiary nitrogen donors from two different DMBDIZ ligands. The DMBDIZ entity acts as a trans exo-bidentate ligand and bridges the nickel ions to form a uniform linear chain with Ni···Ni separation = 8.703 Å. The hydrogen bonding between the acetate anions and the ligands contributes to the enhancement of the structural dimensionality. Variable-temperature magnetic susceptibility measurements (2.0–300 K) reveal the presence of a very weak ferromagnetic interaction between the magnetic centers.     

Studies of consecutive reactions of organic ions in a reversed geometry mass spectrometer

Over thirty consecutive reactions of a type m₁⁺ → m₂⁺ → m₃⁺ have been studied in a variety of organic compounds using a reversed geometry mass spectrometer. Two field free regions allow the separation of the two steps that make up the consecutive reaction sequence. Translational energy release measurements are used in the comparison of m₂⁺ ions formed as a result of a high energy process in the ion source with m₂⁺ ions formed as a product of a metastable decomposition. In some cases the structures of such ions have been found to be different. Examples have also been found where consecutive fragmentations of metastable ions do not occur although, when higher energy ions within the source are studied, the two-step reaction does take place. Furthermore, it has been found that a control over ion internal energy may be achieved by selecting portions of a peak due to the fragmentation of a metastable ion. Unimolecular reactions may then be used to study the reactivity of such ‘energy-selected’ ions; collision induced reactions can be used to study the structure of both the reactive and unreactive energy selected ions.     

Mass spectra of ethenol and its deutero analogues

Ethenol, 1-d-ethenol, O-d-ethenol and Z-2-d-ethenol were prepared by pyrolysis of corresponding 5-norbornenols at 800^°C/2 × 10^?6 Torr. The most important fragments in the electron impact mass spectrum of ethenol are [C₂H₃O]⁺ and CHO⁺ and CH₃˙. The hydrogen atom eliminated from the molecular ion comes mainly from the hydroxyl group (68%) and to a lesser extent from C(1) (25%) and C(2) (7%). The loss of the hydroxyl hydrogen is preceded by rate-determining migration of the hydrogen atom from C(1) onto C(2) to yield CH₃C?OH⁺˙ions that decompose to CH₃CO⁺ and H˙. The loss of deuterium from O-d-ethenol shows a very small primary isotope effect (k_H/k_D=1.07), whereas a significant effect is observed for the loss of hydrogen from 1-d-ethenol (k_H/k_D=1.28). The appearance energy of [C₂H₂DO]⁺ from 1-d-ethenol, AE=11.32 eV, gives a critical energy for the hydrogen loss, E=203 kJ mol^?1, which is 90 kJ mol^?1 above the thermochemical threshold for CH₃CO⁺+H˙. The appearance energy of CDO⁺ from 1-d-ethenol was measured as 12.96±0.07 eV, which sets the barrier to isomerization to CH₃CDO⁺˙ at 1121 kJ mol^?1. The ionization energy of ethenol was found to be 9.22±0.03 eV.     

Synthesis of Pyrido[2,3-d]pyrimidines via the Reaction of Activated Nitrites with Aminopyrimidines

6-Aminouracil and 6-aminothiouracil ( 1a, b ) were reacted with benzylidenemalononitrile 2a to afford the pyrido[2,3-d]pyrimidines 4a, b . On the other hand, the reaction of 1a, b with benzylidene ethyl cyanoacetate 2b result in a mixture of 5a,b and/or 6a,b respectively. Pyrido[2,3-d]thiazolo[1,2-b]pyrimidines 8a-c were synthesized from the reaction of 4b with α-halo compounds to give the intermediate derivatives 7a-c followed by cyclization using 70% H₂SO₄.     

Syntheses of 10-Oxo-10H-pyrido[1,2-a]thieno[3,4-d]pyrimidines and 10-Oxo-10H-pyrido[1,2-a]thieno[3,2-d]pyrimidines from methyl tetrahydro-4-oxo-3-thiophenecarboxylate and methyl tetrahydro-3-oxo-2-thiophenecarboxylate,respectively

A general synthesis of 10-Oxo-10H-pyrido[1,2-a]thieno[3,4-d]pyrimidines and 10-Oxo-10H-pyrido[1,2-a]-thieno[3,2-d]pyrimidines is described. Methyl tetrahydro-4-oxo-3-thiophenecarboxylate ( 13 ) was condensed with 6-aminonicotinic acid ( 18 ) to give 3,10-dihydro-10-oxo-1H-pyrido[1,2-a]thieno[3,4-d]pyrimidine-7-carboxylic acid ( 19 ). Treatment of 19 successively with chlorotrimethylsilane, N-chlorosuccinimide and water gave 10-oxo-10H-pyrido[1,2-a]thieno[3,4-d]pyrimidine-7-carboxylic acid ( 17 ). Methyl tetrahydro-3-oxo-2-thiophenecarboxylate ( 21 ) was converted to 10-oxo-10H-pyrido[1,2-a]thieno[3,2-d]pyrimidine-7-carboxylic acid ( 25 ) by an analogous route.